This invention pertains generally to coatings and particularly to bioactive wax coatings.
The drag of a ship's hull increases significantly from micro to macro hard fouling which results from the attachment of marine organisms, such as bacteria, algae and barnacles, on the hull surface. Even after these organisms are removed, the smoothness of the hull is seriously reduced by the pitting caused by these organisms.
Other submerged structures experience deterioration caused by marine growth or corrosion. Wooden blocks and piers can be destroyed in a few years if left untreated. Many of the traditional treatments, e.g., creosote, create serious environmental problems. Metal structures, e.g., propellers and anchor chains, lose appreciable performance capability or strength through corrosion and marine growth on their surfaces.
One approach to reducing marine growth is coating the surface with a coating toxic to marine organisms. The coating usually comprises a matrix with one or more toxic materials in the matrix.
A frequently used type of matrix is resinous and forms a paint. The disadvantages of paints are their expense, the diminution of their effectiveness in time, the difficulty of mechanically renewing the smoothness of the paint surface, and the frequent corrosive effect of the toxic substances on the metallic hull.
Instead of coating a hull with toxic paint, the hull can be coated with non-toxic paint that is coated with a biocidecontaining wax. Toxic waxes are also used to renew toxic paint surfaces after the paint has lost its toxicity. The wax coating disclosed in U.S. Pat. No. 4,020,200 by Groszek et al. is typical, i.e., a wax with a stable biocide that is insoluble in seawater but soluble in the wax. Another example is the wax composition in U.S. Pat. No. 4,115,130 by Crump et al. which also includes porous minerals to slow the release of the biocide.
The rate of release is important to biocidal coatings because if the biocide is released too quickly an environmental problem is created and the coating becomes ineffective too quickly. On the other hand, the rate of release must be sufficient to maintain the required biocide concentration at the surface of the submerged structure.
The wax compositions in U.S. Pat. Nos. 4,410,363 and 4,293,339 by R. F. Supcoe and T. Radakovich utilize certain halogenated waxes and wax combinations to provide superior adhesion to a submerged surface and retention of the biocide to provide a very durable and effective coating for retarding marine growth on the submerged surface. The wax composition in U.S. Pat. No. 4,293,339 has the additional important advantage of being capable of underwater application. The other wax compositions require the removal of the surface from the water or the water from the surface before an effective coating on the surface is possible, i.e., a coating that is smooth, continuous, uniform and strongly adhering. The disadvantage of the above wax composition is the use of one or more fluoropolymers which greatly increases the cost of the wax coating.
A biocidal wax coating that can adhere strongly to a surface to form a smooth durable coating over a wide range of temperatures, even if the wax is applied under water or on a wet surface, is an important improvement in the technology. If such a wax can be compounded without fluoropolymers, the versatility and cost of this wax would permit a wide variety of uses.